Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine used to generate electrical power includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more fuel nozzles into a combustion chamber in each combustor where the compressed working fluid mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
In a particular combustor design, one or more fuel injectors, also known as late lean or aft injectors, may be circumferentially arranged around the combustion chamber downstream from the fuel nozzles. A portion of the compressed working fluid exiting the compressor may flow through the fuel injectors to mix with fuel to produce a lean fuel-air mixture. The lean fuel-air mixture may then be injected into the combustion chamber for additional combustion to raise the combustion gas temperature and increase the thermodynamic efficiency of the combustor.
The aft injectors are effective at increasing combustion gas temperatures without producing a corresponding increase in the production of NOx. However, the pressure and flow of the compressed working fluid exiting the compressor may vary substantially around the circumference of the combustion chamber. As a result, the fuel-air ratio flowing through the aft injectors can vary considerably, mitigating the beneficial effects otherwise created by the aft injection of fuel into the combustion chamber. In addition, the compressed working fluid exiting the compressor is often directed or channeled around the outside of the combustion chamber to convectively remove heat from the combustion chamber before flowing through the fuel nozzles. As a result, the portion of the compressed working fluid diverted through the aft injectors may reduce the amount of cooling provided to the outside of the combustion chamber. Therefore, an improved system and method for more evenly supplying the compressed working fluid to the combustor through the aft injectors without reducing the cooling provided to the combustion chamber would be useful.